1. Field of the Invention
The present invention relates to a process for regenerating a catalyst of the type used in hydrocarbon conversion processes. More particularly, this invention relates to the use of sulfur dioxide as a stripping agent in processes for regenerating a catalyst comprising fluorosulfuric acid, at least a portion of said catalyst having become deactivated due to the formation of stable catalytically inert species during contact with a hydrocarbon feedstock in an alkylation process.
2. Description of the Prior Art
It is well known in the prior art that as the alkylation reaction proceeds, an organic material will form and will accumulate in the fluorosulfuric acid catalyst phase. The material has been given a variety of names including red oil, sludge, organic sludge, acid oil and the like. This organic material is a natural by-product of acid-catalyzed hydrocarbon reactions such as occur during alkylation and has been described in the literature as a conjunct polymer (see Miron, S. and Lee, R. J., "Molecular Structure of Conjugated Polymers," J. Chem. Eng. Data, Vol. 8, p. 150-160 (1963), the disclosure of which are incorporated herein by reference). These conjunct polymers are complex mixtures of olefinic, conjugated cyclic hydrocarbons that may be formed from any type of hydrocarbon except aromatics. More specifically, they are believed to be cyclic polyolefinic hydrocarbons with a high proportion of conjugated double bonds, no two of which are in the same ring. Five membered ring systems predominate, but larger, and possibly also smaller, rings are believed to be present. The accumulation of this material will ultimately cause the activity of fluorosulfuric acid catalysts to decline until said catalysts cease to exhibit econimic activity. In such cases, depending upon economic factors, the catalyst may be replaced or regenerated to restore desired activity levels.
One method for regenerating catalysts comprising fluorosulfuric acid has been suggested in U.S. Pat. No. 3,766,293, the disclosures of which are incorporated herein by reference. Other methods for regenerating such catalysts are disclosed in copending applications Ser. Nos. 772,636; 772,637; 772,641; and 772,643, all filed on the same date herewith. In each of said regeneration processes, a paraffinic hydrocarbon, e.g., isobutane or normal-butane, is employed as a stripping agent during acid recovery. However, at the temperatures commonly employed in the stripping zone, the acidity of the reagents present therein can effect undesirable reactions, e.g., ionization, dehydrogenation, polymerization and the like, with the hydrocarbon. This results in degradation of the acid and formation of coke. Therefore, it would be desirable to employ a stripping agent that would not undergo such undesirable reactions.